The human vertebrae may be classified as the cervical, thoracic and lumbar sections. The vertebrae are separated by small cartilaginous cushions identified as intervertebral discs. Chronic back problems often manifest themselves due to a rupture or degeneration of these intervertebral discs either as a result of disease, injury or advanced age. When disc abnormalities occur, nerves within or adjacent to the spinal column may become inflamed or impinged resulting in the individual experiencing pain of varying degree and manifestation, diminished flexibility and reduced range of motion.
In order to reduce the pain associated with the movement of the intervertebral joint, surgical intervention is often indicated as a means to alleviate pressure upon the spinal cord while concomitantly stabilizing the associated vertebrae. This involves a surgical procedure to distract the disc and or vertebra, or portions thereof, and the insertion of bone fusing material into the cavity of the opposing vertebra. Corpectomy devices have been developed to help support the spine and maintain the normal spacing between opposing vertebrae. Some of these devices may be packed with fusing material to ensure solid bone growth between the two vertebrae.
Typically, corpectomy devices are pre-manufactured at various heights requiring that a cavity between opposing vertebrae be prepared and distracted to a dimension corresponding to the most suitably sized corpectomy device. The surgical procedure to prepare the implant site can be difficult and lengthy. Moreover, the procedure can increase risk of trauma to the tissues surrounding of the implant site.
Recently, distractible corpectomy devices that have been developed may be used as both a fusion device and/or a means for maintaining intervertebral spacing. Often these implants include a drive means that allows the corpectomy device to be expanded in situ to a size that corresponds to the cavity created when the damaged tissue is removed. The drive means typically includes devices such as gears, threaded rods, and the like, in mechanical engagement so as to expand or contract the device to a necessary distance between the vertebrae. Such constructions are complicated as they must necessarily comprise many moving parts, which likewise make them expensive to manufacture and more prone to failure. Moreover, when elongated to their expanded position, these devices often fail to provide a substantially enclosed cavity capable of retaining bone fusing material therein, which is often used to ensure fusion between the two vertebrae.
Although there are numerous patents directed to both artificial disk implants and expandable corpectomy devices, adapted for insertion and securement within the intervertebral space, the prior art nevertheless fails to teach an expandable corpectomy device which is capable of securely retaining bone growth/fusion materials therein, and which offers a means for simple incremental adjustment, thereby providing an individualized fit.
U.S. Pat. No. 5,171,278, to Pisharodi discloses an artificial disk implant and methods for implanting it, wherein the implant has a member for adapting, in size and shape, to an anatomical space between vertebrae and apparatus for expanding the member to conform to the space. Unlike the present invention, the design of this implant does not provide an internal cavity suitable for retention of fusing material to ensure solid bone growth between the two vertebrae.
U.S. Publication No. 2007/0255408 and 2007/0255409 disclose an expandable, implantable device to provide fixation between or among anatomical structures.
U.S. Pat. No. 6,524,341 discloses a vertebral bone prosthetic device comprising an interior body with an outer surface and a first coupling element thereon configured and dimensioned to be slidably received along a central axis by the exterior hollow body with a bore therein, and provided with an interior surface having a groove and an exterior surface. The device also comprises a fixation ring having inner having a second coupling element thereon and outer surfaces. The fixation ring is configured and dimensioned to be received within the groove of the exterior body for rotational movement about the central axis. Rotation of the fixation ring results in engagement of the first and second coupling elements to thereby prevent relative sliding movement between the interior and exterior bodies.
U.S. Pat. No. 6,176,881 discloses a device for replacing vertebral bones. The device includes an interior hollow body providing a catch mechanism on its outer surface and an exterior hollow body including a hole or bore extending along the central axis which can slide into each other coaxially along a central axis and can be moved in relation to one another in the direction of the central axis. The exterior hollow body also includes at least one elastic element that projects into the bore at its top end reducing the diameter of the bore so that the elastic element latches onto the catch mechanism of the interior hollow body, thereby fixing the length of the device in such a way that it is resistant to compression.
U.S. Pat. No. 6,200,348 discloses a spacer for insertion between two vertebrae having a variable axial length. The spacer comprises a first sleeve-shaped member and a second member which is slidably guided within the first member adjusting the overall length. The members face each other on an axially extending portion having ratchet notch means allowing engagement for displacement to a desired overall length.
U.S. Pat. No. 5,290,312 discloses a prosthetic vertebra having a two shaped components, the second being marginally smaller than the first. The second component accordingly positioned partially axially within the first component allowing movement so that the overall length of the prosthetic vertebra can be established by appropriately moving the second component within the first. A set screw is threadably engageable with the first component and can be tightened against the second component to hold the components axially stationary relative to each other.
U.S. Pat. No. 6,419,705 to Erickson is directed to expandable bone fusion devices and methods of use. In general, a fusion device according to the invention includes a first member and a second member which can be deployed and locked into an expanded configuration to stabilize the adjacent bone during fusion thereof.
U.S. Pat. No. 6,866,682 to An et al., describes a corpectomy device with an inner member telescopingly disposed in an outer member so that the inner member is movable in an axial direction. The inner and outer members are hollow, defining a chamber, and include apertures in communication with the chamber. A locking clip engages the inner and outer members to fix the position of the inner member with respect to the outer member. The longitudinal dimension of the device is adjustable by distracting the inner member so that the inner member extends from the outer member, and subsequently moving the locking clip from an unlocked position to a locked position. Again, unlike the present invention, the design of this implant includes multiple slots which, in the extended position, fail to provide an internal cavity capable of preventing fusing material therein from leaking, thereby resulting in impaired fusion at the insertion site. Moreover, the device requires the use of at least two separate locking means, and the device must be rotated and a set screw inserted therein to secure the locking clip at the desired longitudinal distance. This construction is problematic in that rotation of the implant in situ is difficult.
U.S. Pat. No. 7,029,498 to Boehm et al., discloses a height-variable vertebral body implant having a first, essentially U-shaped or C-shaped cage, and vertebral support surfaces formed on the first cage. The first cage is an inner cage, which is embraced and guided in a telescopic manner by a second, outer U-shaped or C-shaped cage. Further, legs of the inner and the outer cage are aligned such that a continuous lateral opening is obtained, and the inner and the outer cages are mutually fixed in a predetermined final position. The inner cage includes a longitudinally extending elongated hole having a unilateral toothing. In cooperation with an instrument including a complementary toothing, a relative movement and adjustment may be effected between the cages. In addition, a thread bore is formed in the outer cage in a position below the area of the elongated hole to fix a desired adjustment position. Again, this type of construction is undesirable given that it requires in situ alignment of a plurality of parts in constrained and difficult circumstances.
U.S. Patent Pub. No. 2006/0004447 to Mastrorio et al. is drawn to a height-adjustable device suitable for insertion between posterior spinal processes that allow the surgeon to post-operatively adjust the height of the implant. This reference is typical of devices which are fraught with mechanical deficiencies owing to their inclusion of a complicated drive means to separate the ends of the implant in communication with the vertebrae.
SYNTHES® Spine has an expandable vertebral body replacement device entitled the SYNEX™ System. The device has parallel grooves that operate in a ratchet assembly with each step producing about 2.5 mm of distraction.
The aforementioned prior art disclose expandable vertebral implants constructed such that the majority of forces (contracting) from the tissue structures surrounding the joint are placed upon a single gear mechanism. This stress can eventually lead to cavitation of the device and possible damage to the vertebrae itself.
What is lacking in the prior art is an expandable corpectomy device which offers a simple and easily operable means for effecting incremental expansion/contraction of the device and provides a secure closure effective for maintaining the device at a pre-selected degree of expansion/contraction.